1. Field of the Invention
This invention relates to a single crystal pulling apparatus comprising a water-cooling means for cooling the single crystal while it is pulled and, more particularly, to a single crystal pulling apparatus capable of circumventing adverse effects caused by the provision of a water-cooling means, for example, failures of water piping for supplying cooling water to and discharging the same from the water-cooling means.
2. Description of the Related Art
Various methods are available for the production of silicon single crystals for use in semiconductor substrates and, among them, crystal pulling with simultaneous rotation based on the Czochralski method (hereinafter referred to as “CZ method”) is now widely employed.
According to the CZ method, within a chamber of a single crystal pulling apparatus, a seed crystal held at the lower end of a pull shaft is immersed into silicon melt in a quartz crucible and the pull shaft is pulled up while the crucible and the pull shaft are rotated, thereby a silicon single crystal is grown below the seed crystal.
Usually, a method for increasing the diameter of the single crystal or/and a method for increasing a pull rate of the single crystal are generally employed to improve the single crystal production efficiency. Among these, a method for increasing the single crystal pull rate comprises disposing a heat-shielding member around the single crystal which is being pulled up from the silicon melt, so that the radiant heat emitted from the melt in the crucible and from a heater disposed outside the crucible is shut off by the heat-shielding member and the cooling of the single crystal may be promoted accordingly. A method of further promoting the cooling of the single crystal, proposed in Japanese Patent No. 3678129 and Japanese Patent Application Publication No. 2002-121096 comprises disposing a water-cooling means, which is cooled with cooling water inside a heat-shielding member, in such a manner as surrounding the single crystal in a single crystal pulling apparatus equipped with the heat-shielding member.
Japanese Patent Application Publication No. 2005-145764 proposes a cooling device in which a water-cooling means and water piping for supplying cooling water to this water-cooling means and discharging the same therefrom are made of a similar metal, for example copper or stainless steel. Copper is a nonmagnetic material and is high in thermal conductivity, while stainless steel is high in mechanical strength and, in particular, austenitic stainless steel is advantageous in that, in the case of pulling under application of a magnetic field, it is not affected by the magnetic field.